XBoats not only "can skip" intervening systems, but I would argue that they do so on a regular basis.
Here is a map showing all of the possible destinations within Jump-4 of each world on the Express Network within the Jewell, Vilis, Regina, Lanth, Aramis and Rhylanor subsectors.
Worlds with 5+ systems on the Express Network within 4 parsecs (exclusively within the Spinward Marches):
- Efate/Regina (5)
- Boughene/Regina (5)
- Feri/Regina (5)
- Roup/Regina (5)
- Risek/Rhylanor (7)
- Celaphina/Rylanor (6)
- L'oeul d'Dieu/Aramis (5)
- Aramis/Aramis (5)
- Margesi/Rhylanor (5)
If seeing all those extra lines explicitly laid out on the sector map starts to look confusing to you (and it certainly does to me!) then you ought to understand why the Express Boat "lanes" on the map are really just a simplification to help keep the layout presentation of the sector map as simple and uncluttered as possible so you don't have lines crisscrossing everywhere covering up important information all over the place.
The other thing to remember is that just like with TCP/IP packets, communications are not going to be "single pathed" through the network between nodes.
The Express Network is less a "railroad" that stops at every station along the "tracks" and more of a "Worlds Wide Web" of communications traffic between multiple star systems simultaneously. It's only in places like the Vilis and Lanth subsectors where there is only a "single path" for communications to take (Denotam to Garda-Vilis and Ivendo to Ghandi) that you don't have redundant routes available.
For example, a message that arrives at Ghandi/Lanth would get routed through Denotam/Vilis
*AND* Dinomn/Lanth for forwarding on to Extolay/Lanth, since either route would require 2 jumps in order to reach Extolay from Ghandi.
In the Fifth Frontier War context, hostile fleets showing up in either the Lysen/Jewell or Efate/Regina system will cut Express Network contact with the Jewell cluster, since there are no alternate routes across that part of space.
Note that the smartest shortcut across the Lanth subsector possible without an extensive investment in J5/J6 capability would be for the IISS to establish a Scout Base at Pirema/Lanth so as to connect Dinomn to Rhylanor ... reducing the communication time from Regina to Rhylanor through Lanth subsector from 7 jumps to only 3 jumps. Somehow, the IISS hasn't seemed to figure out this bit of simple logistics yet (despite having centuries to work on the problem).